The present invention relates to semiconductor devices with discrete surface mount components such as capacitors, varistors and resistors. More particularly the invention relates to methods of preventing current leakage problems resulting from flux penetration of a device with a ceramic body.
Resistive devices are known in the art, and are described, for example, in U.S. Pat. No. 5,115,221 issued to Cowman on May 19, 1992, and incorporated by reference herein. With reference to FIG. 1, a typical device 10 may include plural layers 12 of a ceramic semiconductor material with electrically conductive electrodes 14 between adjacent layers. A portion of each electrode 14 is exposed in a terminal region 16 so that electrical contact may be made therewith. The electrodes 14 may be exposed at one or both of opposing terminal regions, and typically the electrodes are exposed at alternating terminal regions 16 as illustrated. The exposed portions of the electrodes 14 are contacted by electrically conductive end terminals 18 that cover the terminal regions 16.
Preferably, the terminal regions 16 may be plated with nickel and tin/tin-lead metals to increase solderability and decrease solder leaching. The end terminals 18 may be affixed using a conventional barrel plating method or dipping process. In addition, a rotating drum process may be used. The plating process may create imperfections in the ceramic body creating problems with subsequent performance.
Following installation into an electrical circuit, electrical devices with ceramic bodies have experienced less than desired performance characteristics as a result of current leakage between the end terminals 18. The leakage current flows between the terminals 18 along the surface of the ceramic 12. The leakage current may be enhanced by the interaction between flux from the soldering process and etching or grooves in the surface of the ceramic body 12. The grooves typically develop during the fabrication of the device. For example, during the plating of the metal terminations 18, the surface of the ceramic 12 may become etched with grooves. When the device is installed into an electrical circuit by soldering the terminals, flux from the soldering process may flow into these grooves on the ceramic body creating a flow path for current between the terminals 18 along the surface of the device.
It is known to provide coatings for electrical devices with ceramic bodies. For example, U.S. Pat. No. 5,614,074 issued to Ravindranathan on Mar. 25, 1997, discloses reacting a semiconductor body with phosphoric acid to selectively form a phosphate layer on the body. The electrically insulative phosphate layer is formed prior to the plating process to inhibit formation of conductive terminals other than at the ends of the device. The phosphate layer may be substantially removed during the plating process. However, in some processes the phosphate layer may remain after the plating process is complete. The passivation process used to form the phosphate layer may further etch the surface of the ceramic body. As a result, the phosphate layer does not inhibit subsequent current leakage between the terminals 18.
Accordingly, it is an object of the present invention to provide a novel method that minimizes current leakage between terminals of an electrical device with a ceramic body.
It is another object of the present invention to provide a novel electrical device with a protective layer to minimize flux penetration of the ceramic surface of the device.
It is yet another object of the present invention to provide a novel method of manufacturing an electrical device with a ceramic body that includes a protective layer to minimize flux penetration of the exposed ceramic.
It is still another object of the present invention to provide a novel electrical device with a flux resistant sealer that does not inhibit soldering.
It is a further object of the present invention to provide a novel method of manufacturing an electrical device that includes providing a flux resistant sealer that does not inhibit soldering.
It is yet a further object of the present invention to provide a novel electrical device with a flux resistant sealer that may be applied to the entire device including the terminals.
It is still a further object of the present invention to provide a novel method of manufacturing an electrical device that includes applying a protective sealant to the entire device including the terminals.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.